Start-up of platinum catalyst naphtha hydroforming system



Oct. 27, 1959 J. A. BocK :TAL

START-UP OF' PLATINUM CATALYST NAPHTHA HYDROFORMING SYSTEM Filed April2o, 1955 naphtha charge such, for example, as the 150 to 360 F. fractionof M-C virgin naphtha is introduced from source 7 by pump 8 throughpreheater 9 and transfer line 10 from which the preheated charge may beby-passed by line 11 to the product recovery system during start-upprocedure. In on-stream operation transfer line will discharge throughlines 12 and 13 to reactor 14 along with recycled hydrogen from line 15which is preheated in heater 16. Effluent from reactor 14 passes throughline 17, reheater 18 and transfer line 19 to reactor 20. Efuent fromreactor 20 passes through line 21, reheater 22 and transfer line 23 totail reactor 24. It should be understood that more than threereheater-reactor stages -may be employed in the system.

Effluent from the tail reactor ows through line 25, heat exchanger 26and cooler 27 to separator 23 from which hydroformed product iswithdrawn through line 29y to a stabilizer and/or conventional productrecovery system. A part of the hydrogen withdrawn from the separatorthrough line 30 may be vented through line 31 but usually about 4,000 to10,000 cubic feet per barrel of charge is recycled through line 32 bymeans of circulating compressor 33 to line 15.

Transfer lines 11a, 13a, 19a and 23a may be selectively connected toheader 34 for discharging through line 35 to swing reactor 36, theeffluent from which passes through line 37 to header 38 and thencethrough line 17a to line 17, line 21a to line 21 or line 25a to line 25.With the valves in lines 11, 12, 13a and 19a closed and 4the valves inlines 23, 23a and 11a opened, preheated naphtha may be introduceddirectly to the swing reactor without interrupting circulation of gasesthrough the remaining reactors and a part of the circulating gases maybe passed to the swing reactor. When ori-stream flow is established, thevalves in li'nes 11 and 11a remain closed and the valve in line 12remains open, valves in lines 13, 17, 19, 21, 23 and 25 being open andvalves in lines 13a, 17a, 19a, 21a, 23a and 25a being closed when theswing reactor is cut out of on-stream position. The swing reactor may besubstitutedfor the lead reactor by opening valves in lines 13a, 35, 37and 17a and closing valves 13 and 17. Alternatively, it may besubstituted for intermediate reactor 20 by opening valves in lines 19a,35, 37 and 21a and closing the valves in lines 19 and 21. The Swingreactor may take the place of the tail reactor by opening valves inlines 23a, 35, 37 and 25a and closing valves in 'lines 23 and 25. ItWill thus be seen that each of the reactors may be taken olf-stream forregeneration and replaced by the swing reactor and that, alternatively,the swing reactor may be connected to operate in parallel with any ofthe other on-stream reactors during periods when no 'regeneration isrequired.

In some Ultraforming systems the recycled hydrogen andthe naphtha chargeare heated in the same preheater. In such systems the charge introducedby pump 8 may be introduced by lines 8a and 8b to line 15 just ahead ofheat exchanger 26 during normal operation and may be introduced by line8a and line 8c to the line entering separator 28 during start-up.

Each of the reactors is preferably aluminized and provided with arefractory lining of lowviron content. TheyV may each contain about thesame amount of catalyst although, if desired, the subsequent reactorsmay contain somewhat more catalyst than the initial reactors. Thecatalyst may be of any known type of supported platinum catalyst and theplatinum is preferably supported on alumina; it may be prepared by`compositing a platinum chloride with an alumina support as described,for example, in U.S. 2,659,701 and it preferably contains about .3 to .6weight percent of platinum.

In regenerative systems the ori-stream pressure is usually below about400 p.s.i.g., i.e. in the range of about 200 to 350 p.s.i.g. or more,While in non-regenerative systems the pressure is, usually about 500p.s.i.g. or higher. vThe inlet temperatures to each reactor are usuallyin the range of about 850 to 970 F., e.g. about 920 F., and may beapproximately the same for each reactor although it is sometimesdesirable to employ somewhat lower inlet temperature to the initialreactor than to the remaining reactors. The over-al1 weight spacevelocity may be in the range of about 1 to 4 pounds of naphtha per poundof catalyst per hour. There is, of course, a pressure drop in the systemso that the lead reactor may operate at about 50 to 100 p.s.i. higherpressure than the tail reactor. t

For effecting purging and regeneration of the catalys in any bed, purgegases and regeneration. gases may be introduced through manifold line 39and a selected one of lines 17b, 2lb, 25b and 37b. Such purge andregeneration gases may be selectively withdrawn through lines 13b, 191;,23h and 35b to manifold line 40 from which gases may be vented or flaredthrough line 41. Flue gas from source 42 may be introduced to the systemby cornpressor 43 and passed by lines 44 and 45 through acooler 46 whichis preferably a scrubbing tower into which cool water is introducedthrough line 47 4and from which water is withdrawn through line 48. Thescrubbed ue gas withdrawn from the top of the tower through line 4 9 ispassed by compressor 50 through line 51, heatex'- changer 52, heater 53and line 54 to manifold line 39 when it is desired to introduce ue gasinto the system for purging and/or regeneration. By closing the valve inline 54 and opening the'valve in line 55, the fluel gas may berecirculated through line 56, heat exchanger'SZ and line 45 back to thescrubber.

Methane or other hydrocarbon gas may be introduced as a purging fluidfrom source 57 and line 58 to mani# fold line 39. Either iue gas ormethane from manifold line 39 may be introduced to the inlet ofcirculating compressor 33 by line 5,9. Air may be introduced from source60 by compressor 61 for effecting regeneration and/ or rejuvenation ofthe catalyst. Excess ue gas may be vented from the system duringregeneration fby line 62. Hot hydrogen for stripping hydrocarbons fromcatalyst in a blocked-out reactor may be introduced by line 63 tomanifold line 40 and thence through-one `oflines 13b, 19b, 23b or 3512to the selected reactor." Also,

hydrogen may be introduced from line 15 line 39 by line 64.

In starting up this system in accordance with our in. vention the entiresystem is, ofcourse, first checked for mechanical defects, cleaned out,dried, and the reactors' are charged with catalyst. A layer of aluminaballs* is preferably placed on top of each of the catalyst beds toprevent swirling of the catalyst pellets which might otheri wise lead toabrasion and production of catalyst fines."` Flue gas from source 42 isnext introducedinto the system and passed via 44, 45, 46, 49, 50, 51,52, 53, 54, 39 and 59 to the inlet of circulating compressor 33 and itis thereafter passed through all'of the heaters, transfer lines andreactors to remove all air therefrom, the 'air and ue gas being at thistime purged from the system through line 31. The temperature of the uegas during this purge should be below 200 F. and the pressure ispreferably about atmospheric, i.e. about 5 to l0 p.s.i.g.

After the initial flue gas purge, the system is pressured with flue gasto at least the desired yoperating pressure, e.g. about 350 p.s.i.g., toYcheck for possible gas leaks. After pressure testing, the system isagain depre'ssured by opening the valve-in line 31. Then the valve inline 55 is opened, the valve in line 54 isclosed, methaneor other inerthydrocarbon gas is introduced from source 57 by line 58, line 39 andline-59 to the inlet of circulating compressor 33. As soon as all of-theflue gas has been purged from the system by methane, the valve in line31 1s set to hold a back pressure of about 30 to 200 p.s.i., el'g. aboutp.s.i., and the Vmethane is continuously circul lated through all of the`reactors while gradually `firing the furnaces to supply heat throughheaters 1'6, 1'8 land 22, the swing reactor preferably being connectedin paral-s lel with the tail reactor at ,tllistirrral temperature tomanifold of the circulating methane is slowly increased Ito elect dryingof the catalyst and any further drying of the reactor linings that maybe required. Water thus removed `may be condensed in cooler 27,separated fromthe circulating methane in separator 28 and withdrawntherefrom through line 65, the valve in line 29 being closed at thistime. Any condensate produced during this drying operation may becorrosive and, if desired, auxiliary drying means may be employed toprevent any moisture or corrosive liquid from entering circulatingcompressor 33. The heating up of the reactors should be suflicientlyslow up to about 300 F. so that the gas will not pick up more than about5 mol percent of water. After this `initial drying step, the temperaturemay be increased more rapidly to about 700 F. and circulation should becontinued at this high temperature until no further appreciable amountsof water are removed from the system.

After the system has thus been dried by hot circulating methane, thevalve in line 65 is closed and the valve in line 29 is opened. Thenaphtha preheater 9 is fired and charged naphtha preheated to about 800F. is introduced through by-pass line 11 (the valves in lines 11a and 12being closed) directly to product efuent line 25 from which it passesthrough exchanger 26, cooler 27, separator 28 and line 29 to the productrecovery system for establishing operating conditions therein. If asingle preheater is employed, naphtha charge is introduced at this timeto the separator through `lines 8a and 8c, the valve in line 8b beingclosed.

The pressure of the hot circulating methane stream, if it is not alreadybelow about 200 p.s.i.g., should next be reduced to as low a pressure asis feasible, preferably to a pressure in the range of about 30 to 150p.s.i.g. Ina non-regenerative platinum hydroforming system a smallamount of naphtha charge is then introduced through line 8b or throughthe naphtha preheater 9 and introduced with methane at the defined lowpressure and at a temperature of at least about 650 but notsubstantially higher than 700 F. into reactors wherein the catalyst is-not heated substantially above 700 F. Dehydrogenation of the chargetakes place rather slowly under these conditions but in anon-regenerative system it is important to avoid deposition ofcarbonaceous deposits. When the hydrogen concentration in the recycledgas stream reaches about 80 percent or more and the pressure built up bygenerated hydrogen reaches about 500 p.s.i., the temperature of theincoming naphtha Emay be increased to the desired operating temperature.

In the preferred regenerative hydroforming systemthe catalyst in one ofthe reactors is preferably heated to about 750 to 800 F. and the naphthawhich is introduced into this reactor is preheated to about the same orsomewhat higher temperature so that the generation of hydrogen willlargely be accomplished in a single Vessel. When the swing reactor isemployedfor hydrogen generation and all catalyst beds have been heatedto about 700 F. by circulating methane, the valve in line 23 may beclosed, the valve in line 23a opened and the temperature of heater 22increased to provide a transfer line temperature of about 800 F. so thatthe swing reactor is thus heated to about 750 to 800 F. Next, with thepressure in the circulating methane system below about 200 p.s.i. andpreferably in the range of 30 to 150 p.s.i., the valves in lines 23a and23 are opened, the valve in line 11a is opened while valves in -lines11, 12 and 13a are closed, naphtha vapors preheated to approximately 800F. are introduced directly through lines 34 and 3S to the swing reactorwhile recycled gases are continuously circulated through heater 16,reactor 14, heater 18, reactor 20, heater 22 and reactors 24 and 36 (inparallel), the temerature of these heaters at this time being increasedto bring the temperature of the lead and intermediate reactors up toabout 800 to 850 F. The hydrogen generated by dehydrogenation in theswing reactor will quickly in- 6 crease the hydrogen concentration ofthe circulating gases to about percent or more and the pressure yirlIthe -system may be increased by the generated hydrogen to the desiredoperating pressure. As soon as the circulating gas stream is at leastabout 80 percent hydrogen, the valve in line 12 is opened and the valveinline "11a is closed so that the charge preheated to about 800 F. isnow cut into the hot circulating hydrogen stream. If and whenregeneration of the catalyst in the swing reactor is desired, suffcienthot hydrogen is available for stripping hydrocarbons therefrom via lines63, 40 and 35b afte'r 'which the valves in lines 63, 37 and 25a areclosed. The I'transfer line temperatures of heaters 9, .16, 18 and 22may be increased to the desired level, eg. about 900 to 920 F. and ifthe operating pressure has not already been fattained, it may quickly beattained in this on-stream operation. Thus, carbon deposition on thelead, intermediate and tail reactors is substantially avoided bystarting up with hydrogen produced in the swing reactor. By graduallyincreasing temperature and pressure during this startup procedure, thedanger of encountering preliminary hot spots (apparently caused byundesired hydro'cracking) may be avoided. Since gases are continuouslybeing circulated through the reactors, reheaters and transfer lineswhile hydrogen is displacing methane, there will be no abrupttemperature changes in any part of the system.

Instead of employing the swing reactor for initially generatinghydrogen, the lead reactor, the tail reactor or in fact any of theon-stream reactors may be preheated to a temperature of about 750 to 800F. by raising the temperature of the appropriate heater and the systemmay be brought on-stream by introducing charging stock at about 700 F.to all of the reactors except the preheated reactor for which thestart-up inlet temperature is preferably about 750 to 800 F. With thismethod of startup, line 11a is not required and the preheated naphth'amay be introduced by transfer lines 10 and 12 when'a separate preheater9 is employed or may be introduced into line 15 by line 8b when hydrogenand naphtha are preheated in the same heating coil. In this embodimentone reactor, e.g. the swing reactor, is preferably blocked out duringthe initial start-up and the inlet temperatures to the reactors whichare at about 700 F. should not be increased until the hydrogenconcentration' inthe c irculating gas is at least about 80 percent. Whenthe circulating methane has thus been essentially replaced by hydrogenand the pressure of the circulating gases has been increased to at leastabout 200 p.s.i., all transfer line temperatures may be increased to thedesired Operating level and any further increase in pressure may bebuilt up so that on-stream operating conditions are fully established.In this case, the reactor which was operated at the initially highVtemperature and in whichmost of the carbon deposition has occurred maybe cut out of the system for regeneration and replaced by the reactorwhich was initially blocked out.

The method of effecting catalyst regeneration will be described asapplied to the swing reactor but it will be understood that the sameprocedure may be employed for any one of the other reactors ywhen it isblocked out. When the charge inlet valve in line 35 is closedand whilethe valve in line 37 remains open, hot hydrogen is introduced by line 63to manifold linev40 and thence through line 35h to strip out anyhydrocarbons that may remain in the reactor, this strippedmaterialbeingdischarged through lines 38 and 25a to line 25. Next, thevalve in lines 63 and 37 are closed and reactor 36 is depressured byopening the valve in line 41. Next, the reactor is purged to eliminatehydrogen therefrom either by introducing ue gas from line 54 or methanefrom source 57 via lines 39 and 37b, the purgegases being vented throughlines 35h, 40 and 41. If methane is employed as a purge, it is followedby a flue gas purge and after the flue gas purge, the valve in line 41is closed and introduction of ue gas from source 42 is continued topressure the reactor with flue gas to approximately ,the same pressureas that employed in on-stream processes, i.e. about 300 p.s.i. This iluegas, under such pressure, is circulated through the reactor bycompressor 50 and sufficient heat is supplied to the circulating gas byheater 53 to bring the temperature of the catalyst bed to about 650 to750 F. lpreparatory to initiating regeneration. Next, controlled amountsof air are introduced from source 60 by compressor 61 into thecirculating ue gas stream at a rate to efect combustion of carbonaceousdeposits without exceeding a combustion zone temperature of about 1050F. The hot ue gas leaving the reactor at about this temperature passesby lines 35b, y40 and 56 through heat exchanger 52 and thence throughline 45 to scrubber 46 wherein the gas is scrubbedwith cool water forcondensing and eliminating most of the water formed by combustion ofhydrocarbonaceous deposits. The net amount of ilue gas production isvented from the system through line 62, the valve in which is set tomaintain the `desired back pressure of about 300 p.s.i. The cooled iluegas which is recirculated by compressor 50 may be further dried bypassing through a desiccant bed (not shown) before it is returnedthrough heat exchanger 52 to heater 53 which, during regeneration,maintains a transfer line temperature of .approximately 700 F.

The transfer line temperature of heater 53 is increased to about 950 F.in order to reheat the catalyst bed to thattemperature. If rejuvenationis required (and it usually is not required until the catalyst has beenregenerated many times) the introduction of ue gas is stopped and theintroduction of air is continued so that the catalyst is treated with acirculating air stream at a pressure of about 300 p.s.i. and atemperature of about 950 F. orfmore for a period of about one-half hourto twelve hourslormore depending upon the extent of rejuvenationrequired.

After the regeneration (or after rejuvenation if rejuvenation has beeneffected) the introduction of air is stopped, the system is depressuredby slowly opening thevalve in line 41 and liiue gas is introduced fromsource 42 to purge all oxygen from the swing reactor and from theregeneration system. After the ue gas purge, the system may be purgedwith methane introduced from source 57 through line 37b. The ilue gas(or methane, if employed) may then be purged from the system withhydrogen introduced through lines 64, 39 and 37b. When a methane purgeis employed, however, it is not always necessary to employ a hydrogenpurge.

Next, the valve in line 37b is closed and the reactor is pressured withhot hydrogen introduced by lines 63, 40 and 35b. When the reactor isthus brought to desired operating pressure, the valves in lines 63 and35h are closed and the reactor may be placed ori-stream by openingvalves in lines 35 and 37.

While our invention has been ldescribed as applied to a particularUltraforming system, it should be understood that it is applicable toother types of regenerative platinum catalyst hydroforming systems andit is also applicable to non-regenerative systems such as Platforming.Various alternative arrangements andoperating conditions will be.apparent `from the above description to those skilled inthe art.

` We claim:v

1. VThe method of starting up a platinum catalyst naphtha hydroformingsystem including lead, intermediate and tail reactors, "heating zones, agas separation zone, a compressor and lines for recycling separated gas,which method comprises purging catalyst beds and reactors with an inertgas to remove oxygen therefrom, purging inert gas from the reactors withan unreactive hydrocarbon gas, circulating said hydrocarbon gas throughthe reactors while heating it to increase the reactor temperatures toabout 700 F., introducing preheated naphtha charging stock at atemperature in the range of about700 to 800 F.1into one of the reactorswhile the pressureof the circulating hydrocarbon gas is in the range ofabout 30 to 200 p.s.i.g., continuing the introductionA of naphthacharging stock at a temperature in said range until the hydrogenconcentration in recycled gas reaches about percent and then increasingthe temperature of the introduced naphtha charge to at least about 850F.

2. The method of claim 1 which includes the step of simultaneouslyincreasing the pressure of the recycled gas while the hydrogenconcentration thereof is being increased.

3. The method of claim 1 wherein the unreactive hydrocarbon gas is chieymethane.

4. The method of claim 1 which includes the steps of introducing theunreactive hydrocarbon gas at the inlet of said compressor, passing itthrough said heating zones and reactors, cooling the eftluent gasleaving the tail reactor to condense water and separating water from thecirculating gas in the separating zone.

5. The method of claim 1 which includes the step of initiallyintroducing preheated naphtha charging stock into a reactor which is ata higher temperature than the remaining reactors.

6. The method of claim 5 which includes the step of initially passingpreheated naphtha only through the swing reactor of a regenerativehydroforming system containing such a swing reactor.

7. The method of starting up a platinum catalyst naphthal hydroformingsystem including lead, intermediate and tail reactors, heating zones, agas separation zone, a compressor and lines for recycling gas from saidseparation zone, which method comprises purging free oxygen from saidsystem with a non-combustible gas, purging said noncombustible gas fromthe system by introducing thereto an unreactive hydrocarbon gas,circulating said hydrocarbon gas through the reactors at graduallyincreasing reactor temperatures up to about 650 to 700 F. while removingfrom the circulating gas any water removed from the system by said gas,heating the `catalyst in one of said reactors to a temperature in therange of about 700 to 800 F., introducing preheated naphtha charge intosaid reactor at a temperature in said range and at an initial pressurenormal operating pressure whereby dehydrogenation of naphtha is effectedand the hydrogen concentration in the recycled gas is increased, andincreasing the temperature `of the introduced naphtha to at least about850 F. in all of the on-stream reactors after sutlicient hydrogen hasbeen built up in the recycled gas stream to substantially prevent carbonformation on the catalyst.

8. The method of claim 7 in which the hydroforming system isnon-regenerative and in which the introduced preheated naphtha chargingstock is at a temperature which is initially not substantially higherthan 700 F.

9. The method of claim 7 in which the hydroforming system isregenerative and contains a swing reactor, which method includes thesteps of initially introducing naphtha at a temperature substantiallyhigher than 700 F. into a selected reactor for providing a hydrogenbuild-up in the system and subsequently blocking out said selectedreactor and regenerating catalyst therein.

References Cited in the le of this patent UNITED STATES PATENTS2,184,235 Groll et al Dec. 19, 1939 2,330,462 Weiland Sept. 28, 19432,335,610 Plummer Nov. 30, 1943 2,388,536 Gunness Nov. 6, 1945 2,641,582Haensel June 9, 1953 2,737,477 Hemminger Mar. 6, 1956 2,749,287Kirshenbaum June 5, 1956 2,773,013 Wolf et al Dec. 6, 1956 UNITED STATESPATENT OFFICE CERTIFICATE CF CORRECTION Patent Nm, 2991094230 Goiaober2297:, '3:1959

James L 'Boek 'et elw It is hereby certified that error appears in theprinted. specification of the above numbered pateml requiring correctionand "that the said Letters Patent should read as corrected below.

Coluxrm By line +59 after "pressure" inser um below ma (SEAL) Attest:

KARL H., AXLINE Attesting Gfcer HUBERT C. WA'ISN Commissioner of Patents

1. THE METHOD OF STARTING UP A PLATINUM CATALYST NAPHTHA HYDROFORMINGSYSTEM INCLUDING LEAD, INTERMEDIATE AND TAIL REACTORS, HEATING ZONES, AGAS SEPARATION ZONE, A COMPRESSOR AND LINES FOR RECYCLING SEPARATED GAS,WHICH METHOD COMPRISES PURGING CATALYST BEDS AND REACTORS WITH AN INERTGAS TO REMOVE OXYGEN THEREFROM, PURGING INERT GAS FROM THE REACTORS WITHAN UNREACTIVE HYDROCARBON GAS, CIRCULATING SAID HYDROCARBON GAS THROUGHTHE REACTORS WHILE HEATING IT TO INCREASE THE REACTOR TEMPERATURES TOABOUT 700*F., INTRODUCING PREHEATED NAPHTHA CHARGING STOCK AT ATEMPERATURE IN THE RANGE OF ABOUT 700* TO 800*F. INTO ONE OF THEREACTORS WHILE THE PRESSURE OF THE CIRCULATING HYDROCARBON GAS IS IN THERANGE OF ABOUT 30 TO 200 P.S.I.G., CONTINUING THE INTRODUCTION OFNAPHTHA CHARGING STOCK AT A TEMPERATURE IN SAID RANGE UNTIL THE